Synthesis And Flocculation Properties Of Chitosan Derivatives

The shortage of water resources is a worldwide problem,this technology of wastewater treatment will attract much attention.Among many methods of wastewater treatment,flocculation sedimentation method is one of the mostly used for its low cost,and the flocculation performance was determined by the type of flocculant.In recent years,for traditional flocculants' large dosage,low efficiency,toxic and easy to cause secondary pollution,chitosan and other natural polymer flocculants have been widely studied.Compared with the traditional flocculant and synthetic organic polymer flocculant,modified chitosan flocculant have some advantages,such as a wide range of sources,high selectivity,low toxicity,high efficiency,low price and environmental friendly,et al.It is regarded as an ideal material for water treatment.However,there are still some problems in the use of chitosan as flocculant,for instance chitosan can only be dissolved in acidic aqueous solution,which can not be used in more complex water.Therefore,in this paper,in order to improve the flocculation effect of chitosan and broaden the scope of application of chitosan,the chemical modification method was used to modify chitosan to synthesize a series of novel chitosan flocculant.This thesis includes the following sections:1.Water soluble chitosan derivatives,N,O-carboxymethyl chitosan(CMC),hydroxypropyltrimethyl ammonium chloride chitosan(HACC),N,O-carboxymethyl-hydroxypropyltrimethyl ammonium chloride chitosan(QCMC)were synthesized by reaction of chitosan with methyl iodide,monochloroacetic acid,2,3-glycidyl trimethyl ammonium chloride(GTA)respectively.The modified chitosan derivatives were characterized by Fourier transform infrared(FTIR),Nuclear magnetic resonance hydrogen spectrum(1HNMR),X-ray diffraction(XRD),Environmental scanning electron microscope(ESEM)to observe changes in chemical structure and morphology.On the basis of substitution degree(DS)and yield(P),the optimum synthesis conditions were explored,and with residual turbidity as a benchmark,taking kaolin suspension simulated wastewater,theflocculation performance of the synthetic products were experimental system.The results indicated that,the optimal conditions for the preparation of CMC were as follows: chloroacetic acid dosage 5.7g,NaOH mass concentration 51%,alkalization reaction time 7h,and the reaction temperature 40?,under the above conditions,the CMC O-position degree of substitution(Y1)and N-position degree of substitution(Y2)reached 0.7213 and 0.2857;The optimal conditions for the preparation of HACC were as follows: when the compound emulsifier HLB value was 6.0,volume ratio of oil to water was 1.0:1,initiator amount was 1.5%(based on mass of GTA),reaction time was 5 h,reaction temperature was 60?and mass radio of GTA and CTS was 3.0,the degree of substitution and yield of the product reach the maximum,they were 1.331 and 81.16%,respectively;The optimal conditions for the preparation of QCMC were as follows: the reaction temperature 60?,reaction time 5 h,initiator amount was 1.55%(based on mass of GTA),mass radio of GTA and CMC was 2.0,under the above conditions,the substituting degree of QCMC reached 0.9873.The flocculation test results showed that when the p H=6,dosage of flocculant was 1 mg/L,the residual turbidity of the supernatant reached the lowest.2.The flocculation performance of the chitosan derivatives(CMC,HACC,QCMC)were studied using sanitary waste as the flocculating object.And they were compared with CTS and cationic polyacrylamide(CPAM).The influence of different reaction conditions(dosage,pH,the temperature)on the flocculating effect was also investigated.The results showed that flocculating properties of chitosan derivatives were superior to chitosan and CPAM.In addition,the optimal flocculation conditions were as follows: optimal dosage of CTS,CMC,HACC,QCMC is 8mg/L,pH=6,temperature 20-40?.Among them,the dosage and pH had a great influence on the flocculation,and the effect of temperature on flocculation was relatively small.We can see that,by modification,the flocculation p H range of CTS increased from 4~6 to 4~9,which increased obviously.By comparing the flocculation performance of QCMC,CTS and CPAM,we found that,the removal rate of turbidity of QCMC was increased by4.3% and 9.3%,and the removal rate of COD was increased by 19.8% and32.1%,respectively.The results showed that the flocculation effect of QCMC was the best in the QCMC.3.Compound QCMC and PFS were tested,and the application conditions of the complex flocculant were optimized.The result showed that when temperature was 60?,pH=6,the mass ratio of QCMC to PFS was 1:5,dosage of compound coagulant was 6 mg/L,and under these condition,The removal rate of COD was 96.3%.Compared with QCMC alone,the removal rate of COD was increased by 24.3%.